The preparation of rubbery polymers such as butyl rubber and halogenated butyl rubber is well known and has been commercial for some time. This is generally accomplished in the presence of a Friedel-Crafts catalyst at relatively low temperatures and in the presence of an organic diluent, such as an organic halide. Such processes are generally employed for the preparation of butyl rubbers, generally defined as including a copolymer of about 60 to 99.5% by weight of an isoolefin having from about 4 to 8 carbon atoms, such as isobutylene, and from about 40 to 0.5% by weight of a conjugated multiolefin having from about 4 to 14 carbon atoms, preferably between about 4 and 8 carbon atoms, such as butadiene or preferably isoprene. Halogenated butyl rubbers are also prepared by conventional techniques carried out thereon.
Such polymers are generally prepared in a reactor and then the polymer slurry prepared therein is generally withdrawn from the outlet of the reactor and into a reactor overflow line for transport to the initial phase of the recovery system, generally comprising a flash drum where unreacted monomers and diluent are removed by flash vaporization. It has been found in the past, however, that polymer lumps tend to form on the internal surface of the overflow line and interfere with or plug the flow of this slurry from the reactor to the recovery system. Furthermore, some polymerization continues in the overflow line, producing low molecular weight polymers due to the presence of active catalyst and residual unreacted monomers. This continued polymerization generates heat, which induces agglomeration and thus further aggravates the problem of plugging in the overflow line.
In conventional processes for the production of such rubbery polymers, such as that shown in U.S. Pat. No. 3,023,191 to Tegge et al, and assigned to Esso Research and Engineering Co., the assignee of the present application, it has been known to remove the polymer slurry from the reactor through such an overflow conduit into a flash drum which is maintained at a temperature sufficiently high to vaporize any organic halide present therein. Simultaneously, various hydrocarbon liquids, including hexane, having boiling points above the boiling point of the organic halide diluent are injected into that flash drum so that a substantial portion of the organic halide flashes off overhead and the polymer may then be drawn off in the hydrocarbon solvent from the flash drum in the form of a polymer cement, for further processing. These patents have also taught that a small amount of water, for example up to about 500 wppm (parts per million by weight), can be included in the hydrocarbon solvent in order to assist in deactivating the Friedel-Crafts catalyst present therein, or that a small amount of an oxygenated hydrocarbon such as an alcohol (e.g. isopropanol) can be blended with the solvent or injected separately into the flash drum in order to prevent "after" polymerization therein. Water, for example, could not be employed in the proximity of the reactor outlet because it will immediately freeze in view of the temperatures encountered at that point.
It is also known to feed steam and water into the flash drum itself in order to similarly remove volatile materials and to reslurry the polymer in an aqueous suspension, which can then be removed therefrom. This is shown for example in U.S. Pat. No. 3,257,349 to Johnson, Jr. et al, also assigned to Esso Research and Engineering Co.
In view of the continued problems of plugging and after polymerization which have persisted in such commercial polymerization facilities, there have been considerable efforts to overcome the problems associated with plugging of the slurry flow in the overflow line or passageway from the reactor to the flash drum. These have included an attempt to coat the inside of the overflow line with a polyhaloethylene coating, but such attempts have not been entirely successful. Furthermore, in a commercial butyl plant operated by the assignee of the present invention in Fawley, England, an attempt to flush out the overflow line has been made by injecting the hydrocarbon solvent, such as hexane, into the overflow line at a point in proximity to the outlet of the reactor itself. Some of the products produced by this process, which was not carried out publicly in England, may have been sold in the United States more than one year prior to the filing date of this application. This process, however, was counter-productive in that it tended to induce even greater post-polymerization by the heating created by the warm hexane into the overflow line. These attempts have therefore not been entirely successful and have not been capable of maintaining a free flowing overflow line, of preventing further polymerization therein, or of preventing the concomitant reduction in the quality of the polymer obtained as a result thereof.